Microtubule-associated protein 2 (MAP 2) immunoreactivity in human fetal neocortex

We used a monoclonal antibody to study the immunocytochemical distribution of microtubule-associated protein 2 (MAP 2) in human fetal neocortex between the ages of 16 and 22 weeks gestation. The staining pattern was lamina-specific. Neuronal somata and dendrites in all cortical layers and in the intermediate zone were labelled. Cajal-Retzius cells of layer I, large pyramidal neurons in the inner cortical plate and neurons in the subplate were most strongly immunoreactive. Separate from the underlying cortical plate a thin sheet of small neurons in the inner marginal zone was highlighted by MAP 2 immunoreactivity. The morphologic diversity, density and regional distribution of the interstitial neurons in the subplate was emphasized by MAP 2 staining. In general, the intensity of MAP 2 immunoreactivity in cell somata and dendrites correlated with the degree of neuronal differentiation but the pattern of intracellular staining also varied as a function of laminar position, and presumably cell type.